1. Field of the Invention
The present invention relates generally to writing instruments and, more specifically, to a writing instrument, such as a ballpoint pen, having a rotary cam mechanism for feeding a writing refill of the writing instrument.
2. Background Information
Various types of conventional writing instruments having a structure in which a writing refill is fed by a knocking operation using a rotary cam mechanism have been known as described in U.S. Pat. Nos. 5,413,428, 5,263,786 and 5,004,364. The rotary cam mechanism has a stationary cam formed on an inner face of a barrel, a rotary cam abutting a rear end of a writing refill and engaged with the stationary cam, and a knocking cam inserted in the stationary cam and which moves the rotary cam in an axial direction. The rotary cam mechanism is constructed so that by knocking the knocking cam, the rotary cam is rotated and its engagement position with the stationary cam is changed, by which the writing refill is protruded to a writing position or retracted to an accommodated position within the barrel. More specifically, the stationary cam has a guide groove extending in the axial direction and a slant cam face. The rotary cam has a guide projection which enters the guide groove of the stationary cam and a rotary cam face which engages with the slant cam face of the stationary cam. The knocking cam has an engagement projection which enters the guide groove of the stationary cam and a knocking cam face which engages with the rotary cam face of the rotary cam. The writing refill is urged backward by a spring and its rear end abuts on the rotary cam. Accordingly, the rotary cam and the knocking cam are urged rearwardly by the spring.
When the knocking cam is knocked, the rotary cam advances, the guide projection comes out of the guide groove of the stationary cam, and the rotary cam rotates by the actions of the rotary cam face and the knocking cam face. By this construction and operation, the rotary cam face of the rotary cam engages with the slant cam face of the stationary cam, and the rotary cam is maintained at the advanced position. Since the writing refill is advanced by the rotary cam, the front end of the writing refill protrudes from the front end of the barrel and can be used for writing.
When the knocking cam is knocked again in the writing state, the rotary cam is pressed and advanced by the knocking cam, the slant cam face and the rotary cam face are disengaged, and the rotary cam is further rotated. Then, the guide projection of the rotary cam enters the guide groove of the stationary cam, whereby the rotary cam and the writing refill urged backward by the spring are retracted, and the front end of the writing refill is accommodated in the barrel.
Since the entire body of the rotary cam mechanism is pressed backward by the spring which urges the writing refill backward as described above, the stationary cam forming part of the rotary cam mechanism is integrally formed on an inner wall of the barrel as described in U.S. Pat. Nos. 5,004,364 and 5,263,786, or a cam body including the stationary cam is formed and the cam body is fixed under a detachment-preventing state on the inner face of the barrel as described in U.S. Pat. No. 5,413,428.
Accordingly, the conventional writing instruments require the rotary cam and the knocking cam to be inserted in the stationary cam which is fixed as described above, from the front portion of the stationary cam, whereby the conventional writing instruments having the rotary cam mechanism are constructed so that the front portion of the barrel can be opened. As the structure for opening the front portion of the barrel, a nose cone (tip) is detachably disposed at the front end of the barrel by screwing, or the barrel is constructed so as to be separable into upper and lower parts. Accordingly, when the writing refill is changed, in many cases, the barrel constructed of separable parts must be disassembled, or the nose cone screwed at the front end of the barrel must be detached to open the front end of the barrel. Since such a screwed part is necessarily provided, the nose cone portion becomes large in diameter to some extent, or when the barrel is transparent, the screwed part or the like is seen from the exterior thereof which presents an unsightly appearance. Accordingly, the conventional writing instruments are associated with restrictions in both design and aesthetic appearance.